/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.connector.base.source.reader;

import org.apache.flink.api.connector.source.SourceReader;
import org.apache.flink.api.connector.source.SourceReaderContext;
import org.apache.flink.api.connector.source.SourceSplit;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.connector.base.source.reader.fetcher.SingleThreadFetcherManager;
import org.apache.flink.connector.base.source.reader.splitreader.SplitReader;
import org.apache.flink.connector.base.source.reader.synchronization.FutureCompletingBlockingQueue;

import java.util.Collection;
import java.util.function.Supplier;

/**
 * A base for {@link SourceReader}s that read splits with one thread using one {@link SplitReader}.
 * The splits can be read either one after the other (like in a file source) or concurrently by changing
 * the subscription in the split reader (like in the Kafka Source).
 *
 * <p>To implement a source reader based on this class, implementors need to supply the following:
 * <ul>
 *   <li>A {@link SplitReader}, which connects to the source and reads/polls data. The split reader
 *       gets notified whenever there is a new split. The split reader would read files, contain a
 *       Kafka or other source client, etc.</li>
 *   <li>A {@link RecordEmitter} that takes a record from the Split Reader and updates the checkpointing
 *       state and converts it into the final form. For example for Kafka, the Record Emitter takes a
 *       {@code ConsumerRecord}, puts the offset information into state, transforms the records with the
 *       deserializers into the final type, and emits the record.</li>
 *   <li>The class must override the methods to convert back and forth between the immutable splits
 *       ({@code SplitT}) and the mutable split state representation ({@code SplitStateT}).</li>
 *   <li>Finally, the reader must decide what to do when it starts ({@link #start()}) or when a split is
 *       finished ({@link #onSplitFinished(Collection)}).</li>
 * </ul>
 *
 * @param <E> The type of the records (the raw type that typically contains checkpointing information).
 * @param <T> The final type of the records emitted by the source.
 * @param <SplitT> The type of the splits processed by the source.
 * @param <SplitStateT> The type of the mutable state per split.
 */
public abstract class SingleThreadMultiplexSourceReaderBase<E, T, SplitT extends SourceSplit, SplitStateT>
	extends SourceReaderBase<E, T, SplitT, SplitStateT> {

	/**
	 * The primary constructor for the source reader.
	 *
	 * <p>The reader will use a handover queue sized as configured via
	 * {@link SourceReaderOptions#ELEMENT_QUEUE_CAPACITY}.
	 */
	public SingleThreadMultiplexSourceReaderBase(
			Supplier<SplitReader<E, SplitT>> splitReaderSupplier,
			RecordEmitter<E, T, SplitStateT> recordEmitter,
			Configuration config,
			SourceReaderContext context) {
		this(
			new FutureCompletingBlockingQueue<>(config.getInteger(SourceReaderOptions.ELEMENT_QUEUE_CAPACITY)),
			splitReaderSupplier,
			recordEmitter,
			config,
			context);
	}

	/**
	 * This constructor behaves like
	 * {@link #SingleThreadMultiplexSourceReaderBase(Supplier, RecordEmitter, Configuration, SourceReaderContext)},
	 * but accepts a specific {@link FutureCompletingBlockingQueue}.
	 */
	public SingleThreadMultiplexSourceReaderBase(
			FutureCompletingBlockingQueue<RecordsWithSplitIds<E>> elementsQueue,
			Supplier<SplitReader<E, SplitT>> splitReaderSupplier,
			RecordEmitter<E, T, SplitStateT> recordEmitter,
			Configuration config,
			SourceReaderContext context) {
		super(
			elementsQueue,
			new SingleThreadFetcherManager<>(elementsQueue, splitReaderSupplier),
			recordEmitter,
			config,
			context);
	}
}
